The calculated distance (air line) between Seongnam-si and Cheongju-si is approximately 59 miles respectively 94 kilometers.
By car or train, the actual journey to Cheongju-si is certainly longer, as only the direct route (as the crow flies) between Seongnam-si and Cheongju-si has been calculated here.
Air line (approximately)
94 kilometers
51 nautical miles